A friend of mine did the same thing. He put two supers on top of his brood nest, first placing the inner cover in between, then the top cover. However, he made the mistake of proping up his top cover (he thought he needed more ventilation for this, and of course this acted like a top entrance on the hive, and soon he had every honeybee in the neighborhood robbing out those supers!
Did you have any other means of entrance to the hive other than the main entrance where the guard bees are used to defending?
When you dry supers on the hive you need to set things up as you normally would any other time so the hive is tight against intruders and the only defence that needs to be made is at the normal hive entrance (wherever that is for your hives). The only difference is, you usually put the inner cover between the supers and the brood nest so the girls bring the excess honey down into the brood nest instead of begining to fill the supers again. :D